US 2004/0267207 discloses a drive mechanism suitable for use in drug delivery devices. The drive mechanism may include a housing, a piston rod, and a unidirectional coupling between the housing and the piston rod. The drive mechanism may also include a dose dial sleeve and a drive sleeve, with a clutch mean located there between to prevent relative rotation between the dial sleeve and the drive sleeve when in a coupled state and to permit relative rotation between the dial sleeve and the drive sleeve when in a de-coupled state. The device may further comprise a nut being splined to the dose dial sleeve. The relative rotation between the dose dial sleeve and the drive sleeve thereby causes the nut to precess along a helical thread of the drive sleeve. The position of the nut along the helical thread corresponds to the amount of medicinal product remaining in the cartridge.
EP 0 338 806 discloses a syringe in which energy is stored in a spring during dose setting. During injection the stored energy is released, thereby causing a gear to rotate. The gear is threadedly connected to a piston rod, and rotation of the gear therefore drives the piston rod in an axial direction, thereby causing a set dose to be injected.